The Emperor Strikes Back
Let superstition cease; let the folly of sacrifices be abolished. Whoever, after the publication of this law, continues to sacrifice, shall be punished according to his deserts."
That decree of Emperor Constantius in 341 marked the end of paganism and the beginning of the Christian era. Christianity was no longer a persecuted minority; it began its journey to becoming the official religion of the empire.
The story really begins in 313, when Emperor Constantine gave Christians complete freedom of worship and equality with other religions. Confiscated Christian property was returned, and Christians were again recognized as full citizens of the empire. A series of laws favorable to the church made it plain that Constantine was pro-Christian and anti-pagan.
With this, paganism collapsed. It apparently had been practiced only as a civic duty.
By Constantius's reign (337-61), Christians had become a majority in some areas, and they sometimes persecuted the pagans who had once persecuted them. The government rarely encouraged the behavior, but neither did it try to stop it.
In Alexandria, Egypt, philosopher Demetrius Chytas was convicted of sacrificing to the gods. He argued he was only carrying on a lifelong practice, one begun when such sacrifices were legal, even commanded. Nonetheless, Demetrius was tortured and put under house arrest. In some areas, wearing amulets against diseases and having astrologers cast horoscopes were considered crimes and could result in torture and death.
In his book On the Error of Profane Religions, a famous convert from astrology, Firmicus Maternus, urged rulers to wholly eradicate paganism. "Away with those temple treasures," he wrote. "Let the fire of your mints ...